FIG. 4 shows a structure of a prior art self-alignment type semiconductor laser shown in Applied Physics Letters No. 37, No. 3 (1980) pp 262 to 263. In FIG. 4, the reference numeral 1 designates an n type GaAs substrate, the numeral 2 designates an n type AlGaAs lower cladding layer, the numeral 3 designates a GaAs active layer, the numeral 4 designates a p type AlGaAs upper cladding layer, the numeral 10 designates an n type GaAs blocking layer, the numeral 6 designates a p type AlGaAs upper cladding layer embedded in a groove which is obtained by etching the blocking layer 10 in a stripe configuration. The numeral 7 designates a p type GaAs contact layer, the numeral 8 designates an n-electrode, the numeral 9 designates a p-electrode. The upper and lower cladding layers 4 and 2 have energy band gaps larger than that of the active layer 3, and the blocking layer 10 has an energy band gap smaller than those of the upper cladding layers 4 and 6. Herein, the energy band gaps of the upper cladding layers 4 and 6 may be equal to or different from each other.
The device is operated as follows.
A light generated at the active layer 3 is confined in the active layer 3 by the refractive index difference between the active layer 3 and the upper and lower cladding layers 4 and 2 adjacent thereto. Furthermore, the widening of the light in the direction parallel with the active layer 3, that is, in the transverse direction is restricted by the light absorption and the current confinement by the current blocking layer 10, and thus the light is guided well.
In this prior art semiconductor laser device with such a construction, the widening of the light in the transverse direction is restricted by the light absorption by the n type GaAs current blocking layer 10, thereby resulting in a lower differential quantum efficiency and a difficulty in making higher the output power due to this light absorption loss.